For physical reasons, a substance can assume three different states of aggregation, in which its specific heat may be different. The storage of heat with the specific heat of a substance is most suitably accomplished in the solid and liquid states of aggregation. This method has already found technical application for instance in storage radiators with a stone filling and in water storage boilers. From the viewpoint of thermodynamics it appears more expedient to employ for storage purposes the heat energy required for a change of the state of aggregation, since this amount of heat is in many cases a multiple of the specific heat amount, and the heat exchange takes place at a constant temperature level. Of particular technical interest is the storage of heat by way of crystallization or fusion heat. The heat can be readily exchanged with a storage medium in the liquid or solid state. An obstacle for the technical employ of the fusion heat storage on a major scale is the crystallization delay which may cause the onset of crystallization to shift several degrees Celsius due to the lack of suitable nuclei or starting points.
It is an object of the present invention to provide a method and apparatus as set forth in the introduction, permitting the storage of heat to be accomplished by way of crystallization or fusion heat.
In order to attain this object by the said method, the invention provides that a heat-supplying primary carrier liquid is employed to convert a solid storage medium to the liquid state by supplying fusion heat thereto, and a secondary carrier liquid is employed for recovering heat on demand by causing said secondary liquid to flow in a desired amount through a per se known rotary crystallization drum immersed with a portion of its circumference in the liquid storage medium, so that said storage medium solidifies on the walls of said drum, whereupon the solidified storage medium is again carried into heat exchange relationship with the heat-supplying primary carrier liquid by the rotation of said drum.
According to the invention the problem of crystallization delay is solved by generating the nuclei or starting points for the crystallization by a continuous mechanical action. This mechanical generation of the starting points is accomplished by the rotation of the drum in the liquid storage medium, said drum being comparable in the widest sense with a so-called flaking machine or crystallization drum.
The method according to the invention offers the possibility to employ the fusion heat for storing heat energy on a commercial scale. The primary carrier liquid serves as supplier of heat for introducing heat into the system either continuously or at arbitrary intervals. The storage medium receives and stores the supplied heat. If there is then a demand of heat, the secondary carrier liquid is fed through the drum. The withdrawal of heat by the secondary carrier liquid causes the storage medium adjacent the walls of the crystallization drum to be cooled down. This results in the storage medium crystallizing on the crystallization drum and being subsequently carried in the solid state to an elevation above the level of the storage medium by the continuous rotation of the drum. The drum thus serves not only as a crystallization base, but also for conveying the solidified storage medium toward a location whereat it is to be brought into heat-exchange relationship with the heat-supplying primary carrier liquid. In most cases this location will be defined by a heat exchanger.
At this point the cycle starts anew, since the primary carrier liquid reconverts the conveyed amount of the solidified storage medium to its liquid state in accordance with the available heat supply, the liquefied storage medium being returned to the body of the liquid storage medium.
In order to attain the stated object by said apparatus, the invention provides that a heat-supplying primary carrier liquid is employed to convert a solid storage medium to the liquid state by supplying fusion heat thereto, and a secondary carrier liquid is employed for recovering heat on demand by causing said secondary liquid to flow in a desired amount through a per se known rotary crystallization drum immersed with a port of its circumference in the liquid storage medium, so that said storage medium solidifies on the walls of said drum, whereupon the solidified storage medium is again carried into heat exchange relationship with the primary carrier liquid by the rotation of said drum.
For the proper functioning of the method and apparatus according to the invention it is not essential that the primary carrier liquid be identical to the secondary liquid. Suitable storage media are any substances having their phase conversion point from the solid to the liquid state within the range of the desired storage temperature.
The heat exchanger may be, but does not have to be, located above the storage medium. Depending on the properties of the storage medium, the heat exchanger could for instance be immersed in the storage medium in the form of a coil heat exchanger.
In the apparatus according to the invention, the secondary carrier medium is supplied to the interior of the drum through an inlet, and is then heated within the drum. The heated secondary carrier liquid may then be pumped off or exhausted through an outlet. The introduction and exhaustion of the secondary carrier liquid to the interior of the drum and from the drum, respectively, may be carried out continuously or intermittently.
The drum is rotated during the heat exchange between the storage medium and the secondary carrier liquid. This enables a layer of solidified storage medium to form on the outer surface of the drum during its immersion in the liquefied storage medium. During rotation of the drum, this solidified layer is removed from the drum surface by means of a scraper assembly and conveyed to a portion of the reservoir space whereat the solidified storage medium may be reconverted to its liquid state by the available heat supply of the primary carrier liquid.